This invention relates to apparatus for leveling the working axis of various hand tools specifically electric drills and reciprocating saws. The working axis of a tool, as hereinafter used, refers to the central longitudinal axis of the cutting, boring or drilling element of the tool which is ordinarily disposed normal to a workpiece. For example, the working axis of an electric drill is coincident with the central longitudinal axis of the drill bit.
One type of leveling device in common use utilizes either a circular or cylindrical bubble level. The level is attached to the tool such that alignment of the working axis of the tool may be selectively maintained in either vertical or horizontal datum planes by aligning a bubble within the level in accordance with the design of the level. Prior art provides a single cylindrical bubble level which may be rotatable, for example, U.S. Pat. No. 1,333,559 to Moulton; or, alternatively a pair of circular bubble levels which may be oriented at a 90.degree. angle, for example U.S. Pat. No. 4,141,151 to Jansky. In each case the design is an attempt to permit the working axis of a drill to be selectively aligned either horizontally or vertically. A principle application of the leveling device described herein is the drilling or boring of horizontal or vertical holes or the maintenance of the blade of a reciprocating saw in a vertical or horizontal position. The present invention provides accurate and reliable means for leveling a tool without the use of rotatable bubble levels and incorporating both cylindrical and circular bubble levels and thus obtaining the advantages of each.
Where a single cylindrical bubble level is utilized for leveling the working axis of the drill in a horizontal plane, the same cannot be used for vertically aligning the tool normal to a horizontal datum plane, even if the level were rotatable, because aligning of the tool requires simultaneous two dimensional alignment in intersecting planes which is not possible with a single cylindrical level. Thus, a circular bubble is often used to vertically align the working axis normal to a horizontal datum plane because simultaneous two dimensional alignment is possible. However, where a circular bubble is also utilized for leveling the working axis in a horizontal plane, difficulty is encountered in leveling the tool.
In order to horizontally align the tool, its working axis must be parallel to a reference axis which intersects the cross hairs or bull's eye of the circular bubble level and lies in the plane of the level. Horizontal leveling is accomplished by displacing the working axis within a selected vertical datum plane while centering the bubble with respect to the cross hairs or bull's eye. However, if the circular level is rotated about its reference axis by rotation of the tool about its working axis, the bubble cannot be centered with respect to the bull's eye or cross hairs and thus, the tool cannot be horizontally leveled. For instance, it is common practice to rotate an electric drill about its working axis to facilitate drilling in corners etc. This type of rotational displacement would preclude the horizontal leveling of the working axis where a circular bubble level is utilized as shown in the Jansky reference.
This problem is not encountered where a cylindrical bubble is used for horizontal leveling because only displacement in the vertical datum plane is registered by the cylindrical bubble level despite rotating of the tool. The present invention incorporates a circular bubble level for vertically aligning and a cylindrical bubble level for horizontal leveling thus alleviating the limitations of the prior art.
An additional problem with prior art leveling devices is that they are attached to the tool in such a manner that they are not visible to the operator in all orientations of the tool. For instance the tool may be utilized in a corner such that view of the bubble level is prevented by one or more surfaces adjacent to the working surface. The present invention provides for viewing of the bubble levels from a multiplicity of perspectives. Furthermore, in a preferred embodiment the entire leveling device may be selectively attached to the tool to facilitate viewing of the levels from a multiplicity of perspectives.